1. Field of the Invention
The present invention relates to the construction of a thin structure motor for driving a medium used in a magnetic disk drive unit or an optical disk drive unit, the production method thereof, and the laminated core and the production method thereof.
2. Description of the Prior Art
FIG. 139 shows the stator of the spindle motor for the disk drive unit disclosed in Japanese Patent Publication No. 5-39020. The same Figure shows a stator core 20 formed integratedly by punching the magnetic material and stator coils 2 which are wound around respective teeth of the stator core 20 so that they are contained in respective slots. The spindle motor using this stator core 20 is called inner rotor type. Inside the stator, a rotor and rotor magnets are disposed so as to face the stator. The structure of the inner rotor makes it possible to form a thin structure motor and therefore is suitable for a magnetic disk drive unit and optical disk drive unit which are required to be of compact and thin structure.
FIGS. 140, 141 show a stator of the spindle motor for the disk drive unit disclosed in Japanese Patent Laid-Open No.2-133055 and the magnetic pole tooth of the stator core, respectively. FIG. 140 shows the stator core formed integratedly by punching magnetic material and FIG. 141 shows a magnetic tooth 15 of the stator core, which is wound with stator coil 2. The spindle motor using this stator core is called outer rotor type. Outside the stator, a ring like rotor and rotor magnets are disposed so as to face the stator. A rotor shaft is located in the center of the stator and the rotor shaft is connected to the ring like rotor magnet through a thin circular plate. The spindle motor having such structure also makes it possible to obtain small diameter and thin structure, and therefore is often used as the spindle motor for driving a magnetic disk drive unit or an optical disk drive unit.
FIGS. 142A, 142B, 143A, 143B show part of the stator cores of other spindle motors for the disk drive unit disclosed in Japanese Patent Laid-Open No.2-133055. The spindle motor using this stator core is also of outer rotor type. A difference thereof from the aforementioned outer rotor structure is that part of the respective magnetic teeth can be separated. In the stator core shown in FIGS. 142A, 142B, slot heads 15-2 are inserted into the magnetic teeth wound with the coil 2. In the stator core shown in FIGS. 143A, 143B, respective magnetic teeth 15-3 wound with the coils 2 are inserted into the stator body 15-1.
FIG. 146 shows the structure of a motor for the magnetic disk drive unit and optical disk drive unit disclosed in Japanese Utility Model Laid-Open No.5-86151. This motor is of inner rotor type. As shown in the same Figure, three magnetic teeth constitute a stator core 20 as a single block. Each tooth 15 is wound with the coil 2. The feature of this motor is that the stator core 20 is not disposed in the space in which the head of the disk drive unit moves. On the circumference of the rotor magnet 4, in which the stator core 20 is not disposed, shield yokes 4a are disposed so as to cover the rotor magnet.
FIG. 147 is a partial sectional view showing the stator core and the coil of the spindle motor of conventional floppy disk drive unit disclosed in Japanese Patent Laid-Open No.5-176484. FIG. 148 is a front view of the spindle motor. This motor is of inner rotor type. In the respective Figures, reference numeral 122 designates a stator core formed by punching magnetic material integratedly and numeral 130 designates stator coil wound around the magnetic pole tooth 122a of the stator core 122. The stator core 122 is formed by laminated core in which a plurality of magnetic materials are stacked. Resin layer is formed on the surface of the stator core 122 to insulate between the stator core 122 and the stator coil 130. Reference numeral 112 designates a magnet, numeral 114 designates a shaft and numeral 116 designates a yoke.
FIG. 149 shows the stator core of a conventional thin structure motor disclosed in Japanese Patent Laid-Open No.5-38109. As shown in the same Figure, insulating film 150 is formed on the circumference of the magnetic pole tooth of the stator core 151. That is, the insulating sheet of thermoplastic resin is heated and pressed from both sides to form insulating film 150 on the circumference of the magnetic pole tooth in order to achieve insulation treatment.
The stator shown in FIG. 139 has an integrated ring shaped stator core and therefore, it is difficult to wind the magnetic pole teeth facing inward of the stator with stator coil. In coiling, a nozzle through which wire is run is rotated around the magnetic pole teeth. However, because the inside of the stator core is small, the structure of the winding apparatus is complicated. Additionally, the coiling speed cannot be increased more than 1,000 rpm thereby suppressing the productivity of coiling low. It is impossible to increase the number of slots because the number of slots is restricted by the difficulty of coiling, thereby obstructing the increase of torque and resulting in torque ripple. Although winding wire of the coil neatly contributes to compacting and enhancement of the characteristic and reliability of the coil, it is impossible to wind wire neatly because the space between the stator core and the winding apparatus is very small.
FIG. 140 shows an integrated structure stator. Because the shape of the magnetic pole teeth of the stator core is complicated, it is impossible to wind wire effectively. For the reason, productivity is so low that cost increases and further a special winding apparatus is required.
Although the stator shown in FIGS. 142A, 142B was proposed to solve the aforementioned problem, it is impossible to achieve effective winding of wire if the number of slots is increased to improve the characteristic of the motor. Further, magnetic resistance increases at portions in which divided-stator portions are combined by engagement and air gap is unequalized, so that the characteristic of the motor deteriorates. Although winding procedure is facilitated to the stator shown in FIG. 143, two coil terminals are required for every magnetic pole tooth, thereby the step for connecting coil terminals electrically after coiling is required. Thus, production cost is increased and the reliability of connection is decreased.
By dividing the stator core into blocks in the motor shown in FIG. 146, the difficulty of coiling which is a problem of the inner rotor type is relaxed. However, the step for connecting the coils wound around the respective magnetic pole teeth in respective blocks after coiling is required, thereby increasing production cost and thus decreasing the reliability. Further, because the stator core is divided to blocks, it is difficult to fix the stator core with a certain gap with respect to the rotor magnet. Still further, because the stator core comprises divided blocks, the stator core is not easy to handle or assemble.
In the stators shown in FIGS. 147 and 148, the stator core 122 is of integrated ring structure. Therefore, it is difficult to wind the respective magnetic pole teeth 122a having small gap from an magnetic pole tooth nearby, with the stator coil 130 in the direction in which the stator coil is wound inward of the stator. Namely, when a nozzle through which wire is run is rotated around the magnetic pole tooth 122a for coiling, the structure of the winding apparatus is complicated because the inside of the stator core is small. Additionally, it is impossible to increase the winding speed over 1,000 rpm, thereby suppressing productivity low.
It is impossible to increase the number of slots because the number of slots is restricted by the difficulty of coiling, thereby obstructing the increase of torque and resulting in torque ripple. Although winding wire of the coil neatly contributes to compacting and enhancement of the characteristic and reliability of the coil, in this conventional example, it is impossible to wind wire neatly because the space between the stator core 122 and the winding apparatus is very small.
Resin is integratedly molded to insulate between the stator coil 130 and the stator core 122. In this case, because the process of integrated molding of resin is required, production cost is increased. Further, because resin layer is formed on the stator core 122, additional length of the stator coil 130 is required. Thus, the amount of the magnet wire used for the stator coil 130 increases and therefore, it is impossible to form a thin structure motor.
In the stator shown in FIG. 149, insulating film 150 is formed by heating and pressing the insulating sheet of thermoplastic resin from both sides of the stator core 151 in order to insulate between the coil and the stator core 151. As a result, the insulating sheet and the process for heating and pressing thereof are required, thereby increasing production cost.